1. Field of the Invention
The present invention relates to a loudspeaker broadcasting system and a loudspeaker broadcasting apparatus which can precisely transmit, in a closed space such as a tunnel or an underpass where sound is difficult to damp and a reverberation time is long, broadcasting contents such as guide of shelter broadcasted in its space in an emergency.
2. Description of the Related Art
Heretofore, in a tunnel and underpass (hereinafter referred to as a ┌tunnel┘ simply) and in an institution for managing them, there have been provided a loudspeaker broadcasting system and a loudspeaker broadcasting apparatus for performing emergency broadcasting of shelter guide when a disaster occurs. In an emergency, using speakers placed in emergency parking zones provided at regular intervals (at intervals of about 500 m) , an emergency broadcasting is given to only persons in the emergency parking zones. However, since sound is difficult to damp in the tunnel, a reverberation time becomes long, so that clear sound-reinforcement cannot be obtained. Namely, in case that the speakers are dispersively placed in the tunnel, due to such acoustic characteristic in tunnel that the amplified sound is difficult to damp for a long time, an interference phenomenon of sound occurs among the speakers placed dispersively in the conventional loudspeaker broadcasting system and loudspeaker broadcasting apparatus, and clear sound-reinforcement cannot be performed. Therefore, in JP-A-No. 130999/1985, delay of transmission sound among the speakers placed in the tunnel is corrected by a delay unit thereby to suppress reduction of sound clearness.
However, in the conventional loudspeaker broadcasting system and loudspeaker broadcasting apparatus, only shelter information of the same contents is provided in the tunnel, and it is difficult to perform broadcasting of the different contents according to the condition at each block in the tunnel. The broadcasting of the different contents is, for example, broadcasting for guiding persons, in blocks before a spot where a disaster occurs, to a front emergency exit or a front pithead and guiding persons, in blocks behind the spot, to a back emergency exit or a back pithead.